Method and apparatus for increasing optical density ratios of light valves

ABSTRACT

A method and apparatus is disclosed for increasing the optical density ratio of light valves. The optical density ratio is a measure of the range of light transmission of the light valve, and is the ratio between the optical density with the valve inactivated and the optical density when it is activated. To accomplish this change, the valve is constructed so that it contains more fluid suspension when it is in the off (inactivated) condition to produce a high optical density, and contains less fluid just prior to being activated as well as in the activated condition to controllably decrease its optical density. This increased amount of fluid in the off condition and decrease in the on condition increases the optical density ratio of the valve. Apparatus for incorporating this device into a photographic camera is also disclosed.

United States Patent 1 1 3,756,700 Saxe 1 1 Sept. 4, I973 [5 METHOD AND APPARATUS FOR 3,560,077 2/1971 S00) ct a1. .1 350/160 R INCREASING OPTICAL DENSITY RATIOS I Primary Examiner-David Schonberg OF LIGHT VALVES Assistant Examiner-V. P. McGraw [75] Inventor. Robert L. Saxe, New York, NY. Attorney stephen E. Feldman [73] Assignee: Research Frontiers Incorporated,

Plainview, NY. ABSTRACT [22] Filed: Feb. 9 972 A method and apparatus is disclosed for increasing the optical density ratio of light valves. The optical density [21] Appl. No.: 221,141 ratio is a measure of the range of light transmission of the light valve, and is the ratio between the optical density with thevalve inactivated and the optical density [52] US. Cl. 350/267, 95/53 E, 350/160 R 511 int. Cl G02f 1/30, G03b 9/00 when T0 mmpmh Chang [58] Field of Search 350/160 R 267 266 valve is constructed so that it contains more fluid suspension when it is in the off (inactivated) condition to l /53 produce a high optical density, and contains less fluid just prior to being activated as well as in the activated [56] References Cited condition to controllably decrease its optical density UNITED STATES PATENTS This increased amount of fluid in the off condition and 3,492,062 1/1970 HOOVGI' 350/312 decrease in the on condition increases the optical den sity ratio of the valve. Apparatus for incorporating this device into a photographic camera is also disclosed.

3,119,270 1/1964 2,470,139 5/1949 Campbell 350/267 16 Claims, 5 Drawing Figures SHEET 1 0f PATENTEDSEP. M873 FIG. 3

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METHOD AND APPARATUS FOR INCREASING OPTICAL DENSITY RATIOS OF LIGHT VALVES BACKGROUND OF THE INVENTION In light valves using fluid suspensions a means has been sought to increase the optical density ratio of the light valve (the ratio between the optical density of the valve in the off and on conditions). At present, this ratio is usually in the range of 4 to 5. That is, the fluid is more dense to the passage of white light radiation when the valve is off than when it is on. For example, for an optical density ratio of 4 to 5, in order to obtain a value of 50 percent transmission in the on condition, the valve will have between 6.3 percent and 3.2 percent transmission in the off condition (transmission being an inverse logarithmic function of optical density). A light valve having 3.2 percent to 6.3 percent transmission in the off condition is too trans-missive and is not acceptable for some applications. To obtain a value of close to percent transmission a desirable value would mean having transmission levels of 10-15 percent (with the present optical density ratios) in the on condition. So small an open transmission percent is usually not acceptable. Thus, because of the limited density ratios available, there is no wayto produce both a substantial amount of opening and the desired complete or almost complete closing with light valves that are presently available. Therefore, there is a need toproduce a light valve having a fluid suspension which has an optical density ratio of many times that presently available.

SUMMARY OF THE INVENTION The invention comprises a light valve which is adjustable to produce high optical density ratios. In the off (deactivated) condition, the amount of fluid in the valve is increased so that it substantially blocks all radiation being transmitted through the valve, and just prior to activation and in the on (activated) condition the amount of fluid is decreased so that a substantial amount of radiation is transmitted through the valve.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view of the light valve of this invention.

FIG. 2 is a cross-sectional view of the valve of FIG. 1 taken along line 2-2 of FIG. I with the plates at their maximum separation.

FIG. 3 is a cross-sectional view of the valve of FIG. 1 taken along line 2-2 of FIG. 1 with the plates at their maximum separation.

FIG. 4 is a view of the device of FIG. 1 incorporated in a camera.

FIG. 5 is an exploded view of the camera of FIG. 4.

PREFERRED EMBODIMENT OF THE INVENTION In FIG. I is shown the light valve of this invention. In the conventional manner of light valves operable with fluid suspensions, two substantially parallel flat transparent members 2 and 4 are provided. The members are separated from each other by a distance of, for example, between and 40 mils, to form a gap which is filled with the fluid suspension. The suspension consists of suspended particles of material, such as herapathite, in a fluid vehicle, for example, a solution of nitrocellulose in isopentyl acetate. The particles of herapathite are such that when an electric or magnetic field is applied across the suspension, the particles will become oriented so that the suspension appears transparent and thereby permits radiation to pass through it. When the field is removed, the particles become disoriented by the random action of Brownian movement so that the fluid suspension appears much darker and thereby prevents most radiation from passing through it. As aforementioned, the present ratios representing the relationship between the amount of radiation passing through the suspension in the off and on conditions are such that the suspension can not be made dark enough in the off condition (preferably a transmission of less than 0.001 percent) without also reducing the transmission in the activated condition to a figure that is so low (10 percent or less) that the valve has very limited use.

Also, as aforementioned, it cannot be made to transmit enough radiation in the on condition without also transmitting too much radiation in the off condition to make the valve of little practical use. The main difficulty with overcoming this problem so far has been the inability to produce suspensions which have optical densities in the unactivated condition which are substantially more than 4 to 5 times the optical density of the suspension in the activated condition. This, as aforementioned, is the optical density ratio.

For convenience the following table shows a comparison between values of percent light transmission and the corresponding optical densities.

I: Light Transmission Optical Density 1001 0.00 79.43 0.10 63.10 0.20 50.12 0.30 39.81 0.40 31.62 0.50 25.12 0.60 19.95 0.70 15.85 0.80 12.59 0.90 10.00 1.00 1.00 2.00 0.10 3.00 0.01 4.00 0.00I 5.00 0.0001 6.00 0.00001 7.00 0.000001 8.00 000N001 9.00 0.00(X)000l 10.00

In order to solve the above problem (producing greater optical density ratios) it was discovered that if the cell contained more suspension in the unactivated condition it could be made darker, and if it contained less suspension in the activated condition, it cound be made more transparent. It is in this aforesaid manner that the cell of this invention is built, i.e., a cell which has less suspension when it is activated and more suspension when it is inactivated.

A cell in accordance with this description is the cell in FIGS. 1, 2 and 3. Referring to FIG. I, walls 2 and 4 are substantially parallel flat transparent surfaces. These walls (plates) are constructed such that they can be moved closer together or further apart so as to reduce the size of the gap therebetween and thus, regulate the amount of suspension that is contained therein. One way of reducing this distance between the two plates is simply by moving one plate, plate 4 in the drawing, towards the other plate 2 to thereby cause the fluid suspension to be squeezed out of the cell and into a reservoir. Also, both plates can be physically moved or one or both platescan be made flexible or a third member can be interposed between the plates, or any other suitable method can be used which reduces the size of the gap between the plates.

In FIG. 1 the reservoir is indicated by numeral 6 and is shown in a position above the cell. When it is desired to cause suspension to flow back into the cell in order to increase the amount of suspension in the cell, i.e., when the cell is in the off position (inactivated), plate 4 can be moved away from plate 2 to thereby cause a gravity flow of suspension from the reservoir into the gap between the plates. It should be apparent that increasing the amount of suspension in the cell will increase the optical density of the cell because the path of light through the suspension has been lengthened and there are more suspended particles in the path of light passing through the valve.

It will be appreciated that this is but one of many methods of transferring the suspension from between the plates into a reservoir and of transferring suspension back from the reservoir to the cell gap between the plates. For example, a pump can be provided or a suction system or any of the other known or conventional systems of transferring fluid between two places.

It is important to note that the fluid suspension is usually not completely removed from the cell since it is of course, still desired to have the cell capable of acting as a fluid suspension light valve and therefore suspension must be provided in the valve. The amount of fluid actually moved out of or into the cell between the activated and inactivated condition need only be a small quantity. For example, if there were 10 cc (cubic centimeters) of fluid in the cell in the inactivated condition, there would be 5 to 9 cc removed and thereby l to 5 cc left in the cell in the activated condition or when the cell was to be activated. It will also be appreciated that since the entire fluid suspension is usually not removed, but only a small part of it, this removal can take place extremely quickly so as not to significantly affect the time between inactivation and activation of the cell.

In normal operation, the cell is first usually unactivated, thus having the larger volume of fluid suspension in the cell, and, of course, a greater optical density. A typical cell in this condition would have an optical transmission of only a very small fraction of 1 percent. The cell is then activated which means that after plate 4 has been moved towards plate 2 a voltage is placed cell is inactivated. As the voltage and thereby the field is removed from across the suspension more fluid is moved back into the cell. For example, glass plate 4 is moved away from plate 2 to result in a larger cell volume, to cause fluid to flow into the cell and thereby create a greater optical density in the cell in theinactivated condition. Thus, transmission of a tiny fraction of 1 percent can be produced in the inactivated condition and greater than 60 percent in the activated condition. Stated another way, optical density ratios of 10 to or even larger can be produced. (As aforementioned,

'optical density is inversely related to transmission).

The invention thus produces a light valve which will attenuate almost all radiation in the off condition and also permits a substantial amount of radiation to pass through in the on condition.

Now, referring once again to the structure of the cell. Suitable sealing means is provided around the periphery of the cell. This sealing means can be a bellows like, corrugated material, structure 36, such as that shown in FIG. 1, or any other material such as plastic coated rubber or flexible, inert plastic, which will permit the gap between the plates to be increased or decreased without permitting any of the suspension to leak out of the cell. Some suitable materials for this are corrugated Teflon (polytetrafluoroethylene), and Teflon coated rubber.

To energize the cell, a suitable source of voltage as indicated by numeral 8 in FIG. 1 is provided. This voltage may be applied in the conventional manner to produce a field across the suspension. That is done by means of suitable wiring which connects two area electrodes to the voltage source. These electrodes consist of transparent electrically conductive coatings which are applied to each of the inner surfaces of each of the plates 2 and 4. This is shown more clearly in FIG. 2 where the coatings are designed by numerals l0 and 12. It is noted that a magnetic field may be used to replace or augment the electrical field. Also, the electrodes can be coated with a thin, inert protective material if desired.

The rest of the structure in FIG. 1 shows an actual embodiment of the invention where a mechanism is provided to actuate the cell electrically and also to reduce and enlarge the gap between plates 2 and 4. U shaped member 40 is fastened to plate 4 near its top and bottom as shown in FIG. 3. This member is mounted so that when it is pushed in (to the right in FIGS. 1-3) it decreases and increases the size of the gap between plates 2 and 4 (the size of cell 31). This is more clearly shown in FIGS. 2 and 3. In FIG. 2 the cell is shown at its maximum size, where it contains the maximum amount of of fluid (and thereby there is a maximum amount of particles in the path of light passing through the cell) and in FIG. 3 where the cell is shown at its minimum size (with the sealing bellows 36 collapsed and the amount of fluid and thereby the amount of particles in suspension at a minimum.)

Member 40 is moved in and out by the action of solenoid 42 and springs 38. That is, the energization of the solenoid causes its plunger 43 to push against the curved portion of member 40 to cause it to puch plate 4 towards plate 2 and reduce the size of cell 31, and then the deenergization of this solenoid causes springs 38 which are attached between a fixed support and member 40 to return the member to its original position (where the volume of cell 31 is at a maximum). To energize solenoid 42 a suitable circuit is provided, as shown in FIG. 1. The circuit to the solenoid includes a timing circuit 46, a source of energy 8 (an AC voltage source), and a switch 44, including switch actuating means (a button 45). The depression of button 45 causes energy source 8 to actuate solenoid 42 and cause its plunger 43 to push member 40 and plate 4, (to which it is attached), towards plate 2 and thereby reduce the size of cell 31. This reduction in size will cause part of the fluid suspension in the cell to flow through tube 33 and into reservoir 6. After a sufficient amount of time has elapsed for this to happen, timing circuit 46 causes voltage source 8 to actuate conductive coatings l and 12 on plates 2 and 4 of the cell through suitable electrical connections. The energization of the conductive coatings will cause a field to be applied across the suspension and cause the particles in suspension to become aligned so that light can readily pass through the suspension and the cell. After light has passed through for any desired amount of time, the conductive coatings are deactivated to thereby remove the field from the fluid suspension; this will cause the particles in the fluid suspension to become disoriented through Brownian movement and the cell to become dark once again. The deactivation of the cell can be accomplished by the use of timing circuit 46 if so desired. After a predetermined amount of time, the circuit can automatically deactivate the cell. After the cell is deactivated,

the timing circuit will then cause the deactivation of the I remainder of the circuit and thereby deactivate solenoid 42. Plunger 43 of the solenoid then will no longer be able to hold member 40 in the inward position (to the right in FIG. 1) against the force of springs 38. The springs will then return member 40 to its home position (to the left in FIGS. 1-3) and thus cause plate 4 to be returned to the position of FIG. 2 from the position of FIG. 3. This will cause cell 31 to become enlarged and cause the fluid suspension that was removed from the cell by way of tube 33 and into reservoir 6 to be returned to the cell. The cell will now be very dark because of the increased amount of fluid.

Thus, it will be appreciated that a light valve has been provided which because of the increased amount of fluid suspension in it during the inactivated condition and the reduced amount of fluid suspension in the activated condition will have a much greater optical density ratio than could normally be produced with a fixed amount of fluid suspension and a constant distance between the walls of a cell.

This invention is based on the fact that the more fluid there is in the cell, the more suspended particles there will be in the light path through the suspension, and therefore, the more nearly opaque the cell will appear. As the amount of suspension is reduced and there are fewer particles in the cell, there is less impediment to radiation traveling through the suspension.

It will be appreciated that although a single reservoir has been shown, there can be many reservoirs or the reservoir can simply be part of the gap between the plates which is not used.

FIG. 4 illustrates a camera incorporating the light valve of this invention as a shutter mechanism. Light valves can not be used as shutters in cameras even though they provide the desirable advantage of complete opening of all areas simultaneously, because too much light would be transmitted through the light valve when it was off (inactive) and strike the film. This excess light would partially expose the film and thereby partially destroy it. This would prevent its proper exposure when it was desired to use the film. Thus, a light valve was needed which would provent almost all transmission of light in the inactive condition.

As shown in FIG. 5 which is a partially exploded view of the camera, the light valve 16 is placed in front of the iris aperture 18. The iris aperture being in front of the focusing lens 20 and the film strip 22. All four members are aligned along the line of light path 24 so that when the valve (shutter) is opened, the path of light will go through the shutter, through the iris aperture and be focused by the lens on the film strip.

With the light valve of this invention, as aforementioned, density can be increased to the point where substantially no light passes through the light valve in the off condition and thereby no light will strike the film strip. When it is desired to take a photograph (to expose the film), button 26 shown in FIG. 4 on the camera will be depressed to cause plates 28 and 30 of the light valve shutter to be shifted toward each other in one of the manners aforementioned so that some fluid suspension is removed from the gap between the plates and transferred to a reservoir 34 positioned above the light valve. At the same time, an electrical field is placed across the plates of the light valve (across the suspension) in FIG. 5 by means of a power source by numeral 32. This source can be the same source that actuates the mechanism to move plates 28 and 30 towards each other. The actual mechanism that moves the plates can be a spring drive or motor drive, any other suitable mechanism, or as previously described. When the field is placed across the suspension, the suspended particles therein become oriented so that light is transmitted through the suspension and along the light path to expose the film.

It will be appreciated that a simply delay mechanism as previously described with respect to FIGS. 1-3 is also provided here so that upon the depression of button 26, one plate 28 begins to move towards the other plate to cause the removal of some suspension and then after enough suspension has been removed the delay circuit causes a voltage to be impressed across the plates to cause the particles in suspension to become oriented so that light can then pass through the shutter. This same delay mechanism is then used so that after the predetermined delay time has taken place in the usual camera manner, it actuates the mechanism that moved the plates together, to move them apart and also transfer more suspension into the cell and thereby create a nearly opaque condition when the cell is inactive. It is noted that the advantage of using a light valve as a shutter is that the entire area of the shutter can be exposed at exactly the same time. This could not be done with any of the previous mechanical shutters such as knife edges or vanes. All of these previous mechanical shutters exposed some areas before others and provided non-uniform exposure. However, with the light valve of this invention, a shutter mechanism is provided which exposes all film areas at the same time.

Briefly, to summarize the operation of the camera shutter once again, button 26 is depressed, plates 28 and 30 are moved toward each other to cause suspension to be transferred into reservoir 34. Then the conductive coatings on the plates are activated to cause a field to be applied across the suspension to align the particles so that light passes through the light valve through the iris aperture and is focused by the lens onto the film. Then, after the required exposure time has elapsed, a mechanism causes the deactivation of the suspension and causes plates 28 and 30 to be withdrawn from one another slightly so that the suspension that was removed can be returned to the gap between the plates from the reservoir. The light valve shutter will now prevent substantially all transmission of light through it.

Thus, it will be appreciated that a highly efficient light valve mechanism and camera shutter has been provided.

The terms optical density and optical density ratio, as used herein generally refer to so-called white light" which is a mixture of visible light wavelengths of the various colors of the spectrum, such as one would get from the sun, an incandescent light bulbor a tungsten lamp source. It should be recognized, however, that such terms are also applicable to monochromatic light and radiation other than visible light (such as ultraviolet and infrared).

lt should be noted that the invention herein described can also be used in a display device or a mirror of variable reflectivity.

Also, it will be appreciated that if the cell is not activated until the gap is completely reduced to its smaller size it gains both the darkness advantage of the large gap when the cell is inactive (having to activate a gap of that size would be undesirable since it would require a large voltage), and also the advantage of having to actuate the cell only when the gap is its smaller size which then only requires a small voltage.

It will also be noted that with the device of this invention the transfer of fluid suspension between the reservoir and the cell causes movement which will tend to prevent agglomeration of the particles in suspension. This is discussed in more detail in U. S. Pat. application Ser. No. 174,494.

While specific embodiments of the invention have been illustrated, it will be appreciated that the invention is not limited thereto since many modifications may be made by one skilled in the art that comes within the true spirit and scope of the invention.

I claim:

l. A method of increasing the optical density ratio of a light valve containing a fluid suspension having particles capable of being activated by an electric or magnetic field to change the amount of radiation passing through the valve, comprising the steps of:

removing a portion of the fluid suspension to reduce the amount of particles in the path of radiation passing through the valve to reduce the optical density of the light valve,

activating the particles by application of the electric or magnetic field restoring part of the fluid suspension that was removed to increase the amount of particles in the path of radiation passing through the valve, and deactivating the light valve.

2. The method of claim. 1 including the steps of transferring the removed fluid suspension to a reservoir.

3. The method of claim 2 wherein the step of restoring includes transferring the fluid suspension from the reservoir.

4. The method of claim 3 wherein the fluid suspension contains herapathite.

S. A control device comprising first wall means and second wall means in an electric or magnetic field said first and second wall means defining a cell having a predetermined volume, and adapted to contain a fluid suspension having particles therein which are capable of being activated by an electric or magnetic field to change the amount of radiation passing through the valve said first wall means being mounted to vary the volume of said cell so that the cell will be adapted to contain a lesser amount of suspension and a lesser amount of particles when it is activated by said electric or magnetic field than when it is not activated so that the optical density of the light valve when activated is decreased and when not activated is increased in order to increase the optical density ratio of the light valve.

6. The device of claim 5 wherein said first and second wall means comprise substantially parallel transparent wall members.

7. The device of claim 6 wherein said wall members are connected by a deformable member to define said cell.

8. The device of claim 7 wherein said deformable member comprises a bellows.

9. The device of claim 7 wherein said deformable member comprises poly tetraflourethylene.

10. The device of claim 7 including a reservoir to which the fluid suspension is transferred when said cell is varied to contain a lesser amount of fluid suspenison.

11. The device of claim 10 including activating means to activate said cell.

l2. The device of claim 11 including control means to control said cell so that it is reduced in size to contain a lesser amount of fluid and thereby a lesser amount of particles before the cell is activated by the activating means.

13. The device of claim 12 wherein the control means deactivates said cell after a predetermined time period and causes said cell to increase in size so that it will contain an increased amount of fluid and thereby an increased amount of particles.

14. A camera mechanism comprising:

means comprising an iris aperture a light valve mounted to cover the iris aperture and act as a shutterincluding:

a cell adapted to contain a fluid suspension having particles therein which are capable of being activated by the electric or magnetic field to change the amount of radiation passing through the cell and through the means comprising the iris aperture and said cell being constructed to vary its volume so that the cell can alternatively contain a greater or lesser amount of suspension and a greater or lesser amount of particles means adapted to apply an electric or magnetic field to the suspension to activate the suspension, said means being coordinated with the volume of the cell so that the suspension is activated when the volume is lesser and inactive when the volume is greater, whereby the shutter can be dark in the inactivated condition and pennit a substantial transmission of radiation in the activated condition.

15. The camera mechanism of claim 14 including control means which deactivates said cell after a predetennined time period and causes said cell to increase in size so that it will contain an increased amount of fluid and an increased amount of particles.

16. A light valve including a cell for containing a fluid suspension of minute particles dispersed therein capable of having their orientation changed by an electric or magnetic field to change the transmission of radiation through the suspension, said cell having first and second wall sections spaced apart a distance which is small compared to the lateral dimensions of the sections and means for applying an electric or magentic field to the suspension between said wall sections to 3,756,700 9 10 change the radiation transmission thereof, said first electric or magnetic field so that said field is applied to wall Seem)? being positioned mqvemem with the suspension when said volume is being decreased spect to said second wall section to increase and decrease the volume of said cell and whereby the movement is coorinated with said means for applying an 5 and not applied when said volume is increased.

* Q t t UNlTED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 756 700 Dat d September 4 1973 Inventor(s) Robert L. -Saxe It is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:

In the specification:

Column 1, line 18, "trans-missive should read "transmissive" Column 2, line 48, "cound" should read "could" Column 3, line 20, after "places" the second period should be deleted.

Column 4, line 24, "designed" should read "designated" Column 4, line 40, after "amount" delete second "of" Column 4, line 49, after the second to, "puch" should read "push" Column 5, line 58, "provent" should read "prevent" Column 6 line 24, "simply" should read "simple" In the claims:

Claim 10, column 8, line 18, "suspenison"should read "suspension" Claim 16, column 8, line 66, "magentic" should read "magnetic" Claim 16, column 9, line 5, "coorinated" should read "coordinated" Signed and sealed this 29th day of October 1974.

(SEAL) Attest MCCOY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents F ORM PO-1050 (10-69) USCOMM-DC 6O376-P69 U.S GOVERNMENT HUNTING OFFICE 1969 O356-334, 

1. A method of increasing the optical density ratio of a light valve containing a fluid suspension having particles capable of being activated by an electric or magnetic field to change the amount of radiation passing through the valve, comprising the steps of: removing a portion of the fluid suspension to reduce the amount of particles in the path of radiation passing through the valve to reduce the optical density of the light valve, activating the particles by application of the electric or magnetic field restoring part of the fluid suspension that was removed to increase the amount of particles in the path of radiation passing through the valve, and deactivating the light valve.
 2. The method of claim 1 including the steps of transferring the removed fluid suspension to a reservoir.
 3. The method of claim 2 wherein the step of restoring includes transferring the fluid suspension from the reservoir.
 4. The method of claim 3 wherein the fluid suspension contains herapathite.
 5. A control device comprising first wall means and second wall means in an electric or magnetic field said first and second wall means defining a cell having a predetermined volume, and adapted to contain a fluid suspension having particles therein which are capable of being activated by an electric or magnetic field to change the amount of radiation passing through the valve said first wall means being mounted to vary the volume of said cell so that the cell will be adapted to contain a lesser amount of suspension and a lesser amount of particles when it is activated by said electric or magnetic field than when it is not activated so that the optical density of the light valve when activated is decreased and when not activated is increased in order to increase the optical density ratio of the light valve.
 6. The device of claim 5 wherein said first and second wall means comprise substantially parallel transparent wall members.
 7. The device of claim 6 wherein said wall members are connected by a deformable member to define said cell.
 8. The device of claim 7 wherein said deformable member comprises a bellows.
 9. The device of claim 7 wherein said deformable member comprises poly tetraflourethylene.
 10. The device of claim 7 including a reservoir to which the fluid suspension is transferred when said cell is varied to contain a lesser amount of fluid suspenison.
 11. The device of claim 10 including activating means to activate said cell.
 12. The device of claim 11 including control means to control said cell so that it is reduced in size to contain a lesser amount of fluid and thereby a lesser amount of particles before the cell is activated by the activating means.
 13. The device of claim 12 wherein the control means deactivates said cell after a predetermined time period and causes said cell to increase in size so that it will contain an increased amount of fluid and thereby an increased amount of particles.
 14. A camera mechanism comprising: means comprising an iris aperture a light valve mounted to cover the iris aperture and act as a shutter including: a cell adapted to contain a fluid suspension having particles therein which are capable of being activated by the electric or magnetic field to change the amount of radiation passing through the cell and through the means comprising the iris aperture and said cell being constructed to vary its volume so that the cell can alternatively contain a greater or lesser amount of suspension and a greater or lesser amount of particles means adapted to apply an electric or magnetic field to the suspension to activate the suspension, said means being coordinated with the volume of the cell so that the suspension is activated when the volume is lesser and inactive when the volume is greater, whereby the shutter can be dark in the inactivated condition and permit a substantial transmission of radiation in the activated condition.
 15. The camera mechanisM of claim 14 including control means which deactivates said cell after a predetermined time period and causes said cell to increase in size so that it will contain an increased amount of fluid and an increased amount of particles.
 16. A light valve including a cell for containing a fluid suspension of minute particles dispersed therein capable of having their orientation changed by an electric or magnetic field to change the transmission of radiation through the suspension, said cell having first and second wall sections spaced apart a distance which is small compared to the lateral dimensions of the sections and means for applying an electric or magentic field to the suspension between said wall sections to change the radiation transmission thereof, said first wall section being positioned for movement with respect to said second wall section to increase and decrease the volume of said cell and whereby the movement is coorinated with said means for applying an electric or magnetic field so that said field is applied to the suspension when said volume is being decreased and not applied when said volume is increased. 